Abrasive article



Patente Get. 22, 1940 UNITED; STATES PATENT OFFICE.

ABRASIVE ARTICLE Carl E. Barnes, Worcester, Mass., assignor to Norton Company, Worcester, Mass, a corpora? tion of Massachusetts No Drawing. Application March 19, 1938, Serial No. 197,035 7 50am. (o1. si -29s) This invention relates to abrasive articles and more particularly to such articles made of abrasive grains cemented together by synthetic resin bonds.

5 Grinding wheels and other abrasive articles are customarily made of abrasive grains bonded by a resinoid, such as phenolformaldehyde condensation product. Grinding wheels of this type are often subjected to heavy duty grinding operationswhich generate a considerable amount of frictional heat, and it is desirable that such a bond be resistant to the normal grinding temperatures and that it have a high degree of strength and be capable of tenaciously adhering 15 to the grains and forming a bonded body of sufficient strength to withstand the disruptive stresses set up by centrifugal force and expansion within the wheel due to generatedheat.

A primary object of this invention is tosatisfy ganic bond for abrasive grains which is highly resistant to heat, of great strength, infusible and durable under normal conditions of a grinding operation. Further objects will be apparent in 25 the following disclosure.

It is found that styrene (CaHs-CH=CH:) capable of being polymerized in the presence of abrasive grains to form a bond therefor. But the product is not infusible or sufliciently resistant to the heat of a grinding operation. since it is softened.- at a temperature of about 80 C; .Moreover, when styrene is polymerized by itself and with the aid of suitable catalysts, such as acrylic acid and that the resultant product is satisfactory for use as an abrasive bond and may be economically manufactured. These two polymerizable substances may be mixed and copolymerized in all desired proportions; but-Iprefer that the substances be used only in those amounts wherein the one is soluble in the other so that the-final copolymerized product will be homogeneous-and notcomprise an intermixture of separately polymerized substances.

the above requirements and to provide an or- 'lhe acrylic acid, alpha chloroacrylic acid and methacrylic acid have the property of hastening or activating the polymerization of styrene to such an "extent that the final product may be -made in an economically short period of time; 6

For example, if'styrene is mixed with 25% byvolume of methacrylic acid and with a suitable catalyst such as 0.02% by weight of benzoyl peroxide, this intermixturepolymerizes in, 12 hourstime at a temperature of 50 C. to a hard and heat resistant condition. This product will not soften at any vnormal temperature involved "in a grinding operation and in fact, it will resist the ordinary grinding temperatures.

An abrasive article may, therefore, be made of 15 abrasive grains bonded by a synthetic resin containing styrene copolymerized'with a substance selected from the group consisting-of acrylic acid, alpha chloro-acrylic acid and methacrylic acid. Various types of abrasive grains, such as crystalline alumina, silicon carbide; boron carbide and diamonds may be bonded by these synthetic resins and the grains and bond may beiemployedin any desired: proportions. As examples of suitable bonds, I may employ styrene in suitable in- 25.

termixture with acrylic acid, alpha chloro-acrylic acid or methacrylic acid;

Asan example of one method of formingan abrasive article, such as a wheel, I

' may bond the abrasive grains with styrene and an actiyator, such as acrylic acid, alpha chloroacrylic acid or methacrylicacid, in' their monomeric liquid conditions. The abrasive grains may be placed in a mold in suitable amount and the monomeric substances to be copolymerized are poured over the grains in their liquid poly- -merizable condition and thereafter hardened in place by the application of heat and pressure, if desired; 'The bond may be made,'for example,

of 75% of styrene mixed with 25% of methacrylic 0 acid, together with 0.02% of the catalyst benzoyl peroxide. Various other materials-may be in-' corporated in the bond and grain mixture. .Onemay use fillers of the nature of sand or any other inert substance that does not. adversely 5- affect the polymerization process. The grade of hardness and the structure may be controlled by suitable variation of the amounts of the materials. We may, for example, use 1,656 grams of crystalline alumina abrasive with 365 cubic centimeters of the bond .mixture of which 75% is styrene and 25% is methacrylic acid.' 'A suitable catalyst maybe added. The abrasive material may ,be placed ina mold and the liquid 'monomers poured thereover, The mold may be of any suitable construction, such as a hollow body provided with a cover plate.- The mold and contents are heated to a temperature of about 50 .C. for a pediod of about twelve hours. This causes the bond to set as a hard and infusible material which adheres to the abrasive grains and holds them rigidly in position and thus forms'anarticle of satisfactory abrasive characteristics.

Another method of making an abrasive article involves mixing the two monmeric liquids, styrene and one of the above mentioned polymerizable acids and then subjecting the liquid mixture to a temperature of about 50 C. or higher for a sumcient length of time to cause them.

stances or with any'suitable liquid so that the grains will readily stick to the already polymerized bond particles. Thereafter the intermixture is heated in a mold at a temperature at i Y which the bond is soft, such as about 150 C.,

arid subjected to a-suitable pressure, such as 3 tons per square inch, which is required to form the desired structure. The temperature involvedis that at which the polymerized product will soften.

- An article thus made of styrene mixed with acrylic acid, alpha chloro-acrylic acid or methacryclic acid comprises a bond which is very hard and has a high tensile strength and resists the disruptive forces of a grinding. operation. The bond will not soften at temperatures ordinarily met in grinding and so will serve many useful purposes. It is to be understood that the above matter-1s to be interpreted as illustrative of the invention and not as limiting it to the methods and materials above specified and that the claims are to be interpreted broadly within the scope of my invention. The methods of making abrasive. articles asabove described are claimed in my copending applications Serial Numbers 187,549, filed January 28, 1938; 228,004, filed September 1, 1938; and 316,212, filed January What I claim is new and desire to secure by Letters Patent is:

1. An abrasive article comprising abrasive grains bonded by a synthetic resin containing styrene as the primary ingredient copolymerized with a substance 'of the group consisting of acrylic acid, alpha chloro-arcylic acid and methacrylic acid.

2. An abrasive article comprising abrasive grains bonded by styrene copolymerlzed with acrylic acid. I

p 3. An abrasive article comprising abrasive grains bonded by styrenecopolymerized' with methacrylic acid.

4. An abrasive article comprising abrasive grains bonded by styrene copolymerized with alpha chloro-acrylic acid.

5. An abrasive article comprising abrasive grains bonded by a polymerized substance containing at least of styrene coploymerized with a polymerizable' substance of the group consisting of acrylic acid, alpha chloroacrylic acid and methacrylic acid, which are capable of and proportioned for forming a hard resin that is not soft at the normal grinding temperatures and may be copolymerized at a temperature of C. within 24 hours. Y

CARL E- BARNES. 

